This invention refers to an exhaust gas depurator having a catalytic activity, for internal combustion engines, further acting as discharge silencer.
Exhaust gas depurators having a catalytic activity, for internal combustion engines, are well known In the more customary embodiments, such depurators include a ceramic body traversed in the longitudinal direction by a lot of small rectilinear channels, whose cross section is usually square and amounts to about 1 square millimeter. These channels are separated from each other by walls whose thickness is of about 0.2 millimeter and the surfaces of which are lined by a deposit of platinum. The very high manufacturing cost of such a construction is obvious. The exhaust gases are compelled to pass along said channels having a little cross section, and during this travel they lap on the platinum lining. The platinum exerts on the exhaust gases a catalytic action which aims to oxidize the carbon monoxide and the unburnt hydrocarbons and to decompose the nitrogen oxides As long as the catalyst is in good conditions, the depuration of the exhaust gases may attain the removal of 80% to 90% of the harmful impurities. This effective condition of the catalyst, however, has a relatively short duration, even in the case of carburation engines supplied by gasoline. For such engines a limit run of about 5000 kilometers is generally prescribed, after which the exhaust gas depurator is to be replaced. This is due to the poisoning of the catalyst and, above all, to a clogging of the little channels of the depurator body. Such depurators, on the other hand, are not even mounted on diesel cycle engines, because the sulphur compounds contained in their exhaust gases could put the depurator out of use after some hours.
Very serious disadvantages of said depurators reside, therefore, in the reduced duration thereof with respect to their cost, as well as in their inadequacy for being used with diesel cycle engines. But another serious disadvantage of these depurators resides in the great resistance opposed by the little channels of the ceramic body of the depurator to the passage of the exhaust gases. Such great resistance gives rise to a noticeable counterpressure at the discharge of the engine, and therefore to a serious reduction of its efficiency.
Some improvement has been obtained in these depurators having a catalytic activity by replacing the bored ceramic body by a pleated metal sheet, covered by a catalytic material and adequately folded in order to determine a great number of rectilinear channels of a little cross section. This allows a more economical manufacture, however the disadvantages of an insufficient duration and a high resistance opposed to the flux of gases are not reduced.
The above cited exhaust gas depurators do not provide a specific silencing action, although in practice they somewhat attenuate the noise, only as a consequence of the high resistance opposed to the passage of the exhaust gases.